Molding composition wherein the binder contains polyvinyl acetal, polyvinyl acetate,and vinsol



Patented May 23, 1950 I MOLDING COMPOSITION BINDER CONTAINS POLYVINYL ACETAL POLYVINYL ACETATE, AND VINSOL WHEREIN THE Edward M. Sadowski and William P. Miller, In-

dianapolis, Ind., assignors to Radio Corporation of America, a corporation of Delaware No Drawing. Application August 8, 1946, Serial No. 689,192

10 Claims.

This invention relates to compositions adapted to be moulded into shaped articles with the application of heat and pressure. Although adapted to be moulded into articles of almost any shape, which may serve a variety of useful or ornamental purposes, the compositions are especially useful for making sound records such as, for example, disc phonograph records. This invention is related to co-pending application of Edward M. Sadowski, Serial No. 688,702, filed Aug. 6, 1946, and that of Edward M. Sadowski and Eugene D. OMahony, Serial No. 687,712, filed Aug. 1, 1946.

It has been conventional in the record industry to press or mould disc phonograph records from compositions containing resinous materials and filler. Resinous material used has often been natural shellac. It is now desired, however, to use moulding compositions containing other plastic ingredients in place of either all or some of the shellac in order to make records and other moulded articles having improved properties.

One object of the present invention is to provide moulding compositions which can be substituted for compositions containing shellac as the principal resinous ingredient and which can be used to manufacture moulded articles having properties superior to those made of said shellac compositions.

Another object is to provide plastics moulding compositions which can be used to make articles having improved strength and rigidity as well as resistance to cold flow.

Another object is to provide moulding compositions using a fair proportion of the softer grades of thermoplastic resinous materials having high fluidity when molten and also having relatively low softening" temperatures, which may be used to make sound record discs of high quality.

. Another object is to provide plastics moulding compositions which have excellent moulding properties with a high proportion of filler.

Another object is to provide moulding compositions containing as essential resinous ingredients the polyvinyl acetal resin and polyvinyl acetate.

Still another object is to provide moulding compositions suitable for making phonograph records, which compositions contain a novel type of surface lubricant.

made according to the presentinvention are a polyvinyl acetal resin, such as polyvinyl formal, and a polyvinyl acetate synthetic resin. These materials are tough and, moreover, have the very desirable property of being miscible with many other thermoplastic resinous materials which are less expensive. They are preferably used with a fairly high proportion of filler although the amount of this latter ingredient may vary over a wide range.

Other desirable properties are added to the present compositions by using, in addition to the two synthetic resinous ingredients mentioned above, varying amounts of a third type of resinous material. This latter material is added principally to enhance the moulding properties of the compositions but improved physical properties of the moulded product are also introduced by its use. This third resinous ingredient may be any one or more of a rather large group of thermoplastic resinous materials which vary widely as to their chemical nature. All of them, however, have the property of being highly fluid when molten and they have relatively low softening points. Their softening points as measured by the well known ball and ring method may range from about C to about C. This group of resins includes both natural and synthetic materials and also encompasses within its scope some resinous substances commonly described as asphalts and pitches. A few of the synthetic resins which fall within this category are a polymerized resin which is the gasoline insoluble, aromatic hydrocarbon soluble resinous extract of pinewood, coumarone-indene resins and many phenolic resins in the A or B stages such asthe incompletely condensed phenol formaldehyde resins. Some of the natural resinous materials found suitable are rosin, rosin esters, hydrogenated rosin and resins which are distillation products of sugar cane. Pitches derived 3 from wood tar or coal tar may also be used as well as various asphalts such as gilsonite. It is only essential that these materials have softening points within the range specified above and that they be highly fluid when molten. Shellac, itself, may be used in this part of the composition although a resin such as the said resinous extract of pinewood above referred to, which may be mixed with hardwood pitch, is preferred.

Since the compositions are to be used in making moulded articles, it is desirable to incorporate a suitable mould lubricant to prevent sticking to the mould surfaces. For this purpose, a. metal stearate such as zinc stearate is preferred although other metal soaps of the long chain fatty acids such as palmitates or oleates may be substituted. Alternatively, the fatty acid, itself, may be used instead of the metal soap.

In order to adapt the compositions to various moulding purposes, other ingredients may be added such as fillers or extenders, waxes, dyes, pigments, etc. To adapt the compositions specifically calls for the making of phonograph record discs, anti-friction materials such as waxes have been found desirable. These may be natural waxes, such as carnauba, montan, or Ceranova, or synthetic waxes, such as microcrystalline hydrocarbon waxes and modified fatty acid esters. The chemical composition of the wax which is used is not particularly important. Almost any of the harder waxes may be used providing it is compatible with the resinous ingredients.

It has also been found that in lieu of one of these waxes, a material such as polyethylene may be used. The function of the anti-friction compound in a record composition is to provide a thin film of surface lubricant which lowers friction between the playing surface and the phonograph needle, thereby improving wear. Although polyethylene is regarded as a somewhat elastic substance, it has been found that it .provides a degree of lubrication equal to or better than most waxes. As a pigment, carbon black may be used although this may be changed if a color other than black is desired in the finished product. Oil soluble dyes and pigments, for example, will do equally well. The proportion and kind of filler which may be used in the compositions varies widely, depending mainly upon the use to which the moulded product is to be put and also, to a, degree, on the resinous part of the composition. In general, the amount of filler may vary from 45 to 80 percent by weight of the total composition. In compositions to be used for making phonograph records, the preferred amount of filler is 65-75 percent. For general purpose moulding powders this range may be widened to' from 50 to 80 percent. These ranges hold for the compositions containing all three types of resinous ingredients. If the third type, that is, the low melting highly fluid resin type, is omitted, the percentage of filler is preferably lower and may be around 45 percent.

Many different kinds of fillers may be used. For making phonograph records, it is preferred to use finely powdered mineral products such as limestone or slate flours, powdered silica, diatomaceous earth or clays. Not as desirable but still permissible is the addition of smaller percentages of fibrous fillers such as cellulosio flocks, including cotton flocks or mineral fibers such as those made of asbestos, mineral wool, or glass. For general purpose moulding powders higher percentages of the fibrous fillers may be used and wood flour may be used in place of the mineral fillers.

An example of a typical formulation especially suitable for moulding disc phonograph records is as follows:

To make commercially usable moulding powders out of the above and similar formulations, the ingredients are powdered and dry-mixed and after suitable pro-blending are charged into a Banbury mixer. When mixing is completed in the Banbury, the materials are dumped onto sheeter rolls and formed into sheets which can be ground up to form a moulding powder or cut irliliio blocks for moulding from a so-called bisc .1!

when used for moulding records, the "biscuit may be pre-heated on a steam table at 140 pounds steam pressure. The heated biscuit" is then placed in the stamping press and moulded under 1800-2000 pounds per square inch pressure. The

temperature during the forepart of this stamping operation is about 230-260 F. The moulded product is rapidly cooled while still under pressure and is removed while at a temperature of 90-100 F. When the softer type of resinous material is not used, the moulding temperature must be higher and the pressing cycle is longer.

In these compositions, it is possible to use a considerable range of each ofthe resinous in gredients. The amount of polyvinyl acetal resin may vary between 2-6 percent, the preferred content for low cost and best wearing properties being around 3.5 percent. The polyvinyl p acetate content may vary from 1-10 percent,

the preferred amount from the. standpoint of strength and cost being around 2.5 percent. The polyvinyl acetal resin may be either the formal, the acetal or the butyral and is made by partially hydrolyzing the polyvinyl acetate and reacting with the corresponding aldehyde.

The softer thermoplastic resinous material may be omitted entlrely or may be present in any amount up to about 25 percent by weight of the total composition. The preferred content of this ingredient is about 18.5 percent and this may be made up of a single material or a mixture of two or more selected from along list from which examples have been already given.

The percentages mentioned are all by weight and are for compositions in which a filler constitutes the major proportion of the composition. As the percentage of filler becomes lower, the

percentages of the plastics with respect to the total composition will, of course, be much higher although the ratio of the three types of resinous ingredients will remain about the same with respect to each other.

The amounts of the other lesser important ingredients of the present compositions may alsobe varied to a considerable extent. The surface lubricant comprising either Wax or polyethylene may range from to about 3 percent, the preferred amount being about 1 percent. The plasticizer may vary from about 0.5 to percent in those compositions using all three types of resinous ingredients, and, besides being orthonitrodiphenyl, may be orthoaminodiphenyl, tricresyl phosphate, dibutyl phthalate; dioctyl phthalate, drying oils such as linseed oil or many other compounds which have been well known as plasticizers for the types of resins involved. In those compositions omitting the third type of resinous ingredient the amount of plasticizer must be considerably higher to retain adequate moulding properties. The carbon black content usually ranges from 0 to about 3 percent, the preferred amount being 2.5 percent, especially in record compositions. The fatty acid or fatty acid metallic soap used as a mould lubricant may vary from 0 to about 2 percent, the preferred amount being about 0.5 percent.

Although specific ranges of ingredients have been fully described above, it is not desired to be limited to these. Larger amounts of the minor ingredients may be added, for example, although there is no particular advantage in doing so since the product will not be improved and may even be less satisfactory.

Compared to moulding compositions containing shellac as the principal resinous ingredient, the compositions of the present invention produce moulded products having to percent increase in fiexural strength, higher bursting strength and they have wear qualities equal to or better than essentially shellac compositions.

These new compositions have been found to be superior in certain respects to those using only the polyvinyl acetal resin with one or more of the softer thermoplastics. When the polyvinyl acetate is not present, records made of these compositions possess good strength but lack the proper flow qualities unless the soft resin content is increased to the point where the wearing qualities become very poor. The compositions containing only the polyvinyl acetate with the softer thermoplastics produce moulded articles which are not as strong and which are somewhat poorer in wear.

There have thus been described improved moulding compositions comprising polyvinyl acetal resins, a polyvinyl acetate and preferably, but not necessarily, one of the cheaper and softer grades of thermoplastic resinous materials. These compositions preferably contain at least a mould lubricant and may in addition contain other modifiers such as dyes or pigments, surface lubricants, fillers and plasticizers. These compositions may be used to mould any desired article but are especially valuable in making discs in the surface of which a spiral sound track is either simultaneously impressed or impressed after the disc is made. The compositions may be made up in finely powdered form and mouldings may be made directly from this powder. Or, the powder may be premoulded in the form of blocks or biscuit of standard shape and this biscuit then placed into the final mould to be formed into the ultimate shape with the application of heat and pressure.

a plasticizer, up to about percent by weight of the gasoline insoluble, aromatic hydrocarbon soluble resinous extract of pinewood up to 2 percent by weight of a mould lubricant from the class consisting of long chain fatty acids and long chain fatty acid metallic soaps, up to 3.-

percent by weight of a, wax, and 65-75 percent by weight of a filler.

2. A composition according to claim 1 in which said first mentioned polyvinyl resin is polyvinyl formal.

3. A composition according to claim 1 in which said first mentioned polyvinyl resin is polyvinyl acetal.

4. A composition according to claim 1 in which said first mentioned polyvinyl resin is polyvinyl butyral.

5. A phonograph disc record made up of a composition comprising 2-6 percent by weight of a polyvinyl acetal resin from the class consisting of polyvinyl formal, polyvinyl acetal and polyvinyl butyral. 1-10 percent by weight polyvinyl acetate, 0.5-5 percent of a plasticizer, up

to 25 percent by weight of the gasoline insoluble, aromatic hydrocarbon soluble resinous extract of pinewood, and 65-75 percent by weight of a tiller.

6. A phonograph record according to claim 5 in which said first mentioned polyvinyl resin is polyvinyl formal.

7. A phonograph record according to claim 5 in which said first mentioned polyvinyl resin is polyvinyl acetal.

8. A phonograph record according to claim 5 in which said first mentioned polyvinyl resin is polyvinyl butyral.

9. A moulding composition suitable for making phonograph records, comprising 25.5 percent by weight polyvinyl acetal, 17.5 percent by weight polyvinyl acetate, 2.0 percent by weight carbon black, 45 percent by weight fillers, 1.0 percent by weight polyethylene, and 9 percent by weight plasticizer.

10. A moulding composition suitable for making phonograph records, comprising 25.5 percent by weight polyvinyl acetal, 17.5 percent by weight polyvinyl acetate. 2.0 percent by weight carbon black, 45 percent by weight fillers, 1.0 percent by weight wax, and 9 percent by weight plasticizer.

EDWARD M. SADOWSKI. WILLIAM P. MILLER.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS 

1. A MOULDING COMPOSITION SUITABLE FOR MAKING PHONOGRAPH RECORDS COMPRISING 2-6 PERCENT BY WEIGHT OF A POLYVINYL ACETAL RESIN FROM THE CLASS CONSISTING OF POLYVINYL FORMAL, POLYVINYL ACETAL AND POLYVINYL BUTYRAL, 1-10 PERCENT BY WEIGHT POLYVINYL ACETATE, 0.5 TO 5 PERCENT BY WEIGHT OF A PLASTICIZER, UP TO ABOUT 25 PERCENT BY WEIGHT OF THE GASOLINE INSOLUBLE, AROMATIC HYDROCARBON SOLUBLE RESINOUS EXTRACT OF PINEWOOD UP TO 2 PERCENT BY WEIGHT OF A MOULD LUBRICANT FROM THE CLASS CONSISTING OF LONG CHAIN FATTY ACIDS AND LONG CHAIN FATTY ACID METALLIC SOAPS, UP TO 3 PERCENT BY WEIGHT OF A WAX, AND 65-75 PERCENT BY WEIGHT OF A FILLER. 